In motor vehicle power steering gears such as described in U.S. Pat. No. 4,454,801, issued Jun. 19, 1984 and assigned to the assignee of this invention, manual effort applied to an input or spool shaft of the gear is reacted to an output element or pinion head of the gear through a torsion bar which twists through an angle proportional to the applied effort. A control valve of the steering gear has a valve spool rotatable with the spool shaft and a valve body around the valve spool rotatable with the pinion head. Throttling orifices defined between the valve body and the valve spool open and close to regulate a steering assist boost pressure in accordance with the relative angular positions of the valve body and the valve spool corresponding to the angle through which applied manual effort twists the torsion bar. Close tolerance between the valve body and the valve spool minimizes fluid leakage around the throttling orifices. To minimize valve hysteresis attributable to rubbing or binding of the valve body against the valve spool due to minor runout or eccentricity of the valve spool relative to the pinion head, the valve body is connected to the pinion head through a simple universal joint consisting of a radially oriented spherical pin on the pinon head received in a cylindrical socket in the valve body.
U.S. Pat. No. 5,119,898, issued Jun. 9, 1992 and assigned to the assignee of this invention, describes a variable effort power steering gear having a control valve substantially as described in the aforesaid U.S. Pat. No. 4,454,801 and an electromagnetic apparatus for varying the centering force of the torsion bar. The electromagnetic apparatus includes a magnet ring connected to the spool shaft, a pole piece connected to the valve body at the opposite end thereof from the pinion head, and an exciting coil for inducing electromagnetic torque between the magnet ring and the pole piece. A second radially oriented pin on the pinion head diametrically opposite the aforesaid radially oriented pin is closely received in a slot in the valve body to minimize binding between the valve body and valve spool due to reaction of electromagnetic torque through the valve body. Because the second radially oriented pin limits the degrees of freedom between the valve body and pinion head afforded by the simple universal joint consisting of just the spherical pin and cylindrical socket, more precise and expensive manufacturing techniques are required to achieve acceptably low valve hysteresis.